This invention relates to line burners, and particularly to a line burner having a fuel gas manifold for providing fuel gas to be burned to produce a flame and systems for supplying combustion air to both of the upstream and downstream sides of the fuel gas manifold and for removing inert gases from the flame.
Conventional line burners are suited for regular drying and flue gas cleaning processes and similar processes when the air flow contains sufficient oxygen. See, for example, U.S. Pat. No. 4,340,180 to Belknap et al. relating to a nozzle mixing line burner. If this is not the case and a high content of H.sub.2 O and CO.sub.2 is present, conventional line burners are known to fail or operate in an unsatisfactory manner. Such circumstances occur, e.g., in power plants where the process air must be reheated before it passes over a catalyst for reduction of the NO.sub.x content. Due to ever more stringent regulations for the operation of power plants, for instance with hydrogen sulfide washers, there is a shortage of suitable systems for assuring a sufficient reduction of the NO.sub.x content.
The problem underlying the invention is to provide a burner that operates properly under unfavorable conditions, especially with process air having a high CO.sub.2 content.
This problem is inventionally solved in that each fuel gas manifold is arranged in a burner housing so as to be sandwiched between a primary and secondary combustion air flow channel and that extension plates are connected to the burner housing to help remove inert gas from the region of the burner housing containing the flame.
What is accomplished through the extension plates in a surprisingly simple and safe way is that the flame generated by the line burner is protected from being smothered by inert gas associated with combustion air, thus assuring favorable conditions for a complete combustion. These expansion and extension plates provide sort of a chimney effect so that a backup of the inert gas is safely avoided. The specific routing of the combustion airflow in the area of the fuel gas manifolds has a multiple effect insofar as the fuel gas manifolds are favorably cooled by the flow of combustion air, with the flame being protected at the same time by the combustion air flow sweeping around it, thus preventing inert gas from penetrating into the area of the burner or flame. But assured as an additional effect, surprisingly, is most of all a limitation of NO.sub.x production, since the combustion occurs substantially in two steps. Namely, the combustion occurs in the area of the fuel gas orifices in an orifice plate and situated between the fuel gas manifolds at the point where the combustion air flow, after sweeping across the fuel gas manifolds, returns to the area of the flame, as sort of an afterburn.
With the present invention, it is thus possible in a surprisingly safe way to heat process air with a high CO.sub.2 and H.sub.2 O content, also under unfavorable conditions in the realm of power plants, to a degree such that they can subsequently be passed across the catalyst and brought in contact with it in order to filter off further pollutants safely, so that optimally cleaned flue gases can be passed into the atmosphere.
According to the present invention, a line burner is provided for mixing fuel gas and combustion air to produce a burnable mixture. The line burner includes a burner housing, a pair of fuel gas manifolds situated to lie in spaced apart relation inside the burner housing, and means for supplying fuel gas to the pair of fuel gas manifolds. Means is also provided for mounting the pair of fuel gas manifolds in the burner housing to form a primary airflow channel located between the fuel gas manifolds and a secondary airflow channel located between at least one of the fuel gas manifolds and the burner housing. Each fuel gas manifold is arranged to extend longitudinally along a length of the burner housing. Each fuel gas manifold is formed to include a plurality of fuel gas ports discharging laterally into the primary airflow channel and toward the opposite manifold to provide streams of fuel gas for use in combustion.
The line burner further includes first means for supplying combustion air via the primary airflow channel provided in the burner housing to an upstream side of the fuel gas ports formed in the at least one fuel gas manifold. Combustion air supplied by the first means mixes with the streams of fuel gas discharged through the fuel gas ports in a first air and fuel mixing region. Second means is also provided for supplying combustion air via the secondary airflow channel formed in the burner housing to a downstream side of the fuel gas ports formed in the at least one fuel gas manifold. Combustion air supplied by the second means mixes with a mixture developed in the first air and fuel mixing region in a downstream second air and fuel mixing region. In operation, a first stage of combustion occurs in the first air and fuel mixing region and a second stage of combustion occurs in the second air and fuel mixing region.
In preferred embodiments, the line burner further includes an orifice plate arranged to extend longitudinally along the length of the burner housing between the fuel gas manifolds. The orifice plate is formed to include air orifices therein for providing streams of combustion air transverse to said fuel gas streams directed laterally from the fuel gas ports. The orifice plate is fixed to lie in the primary airflow channel upstream of the first air and fuel mixing region. The second means provides an air-conducting passageway in the burner housing that is configured to bypass the orifice plate so that combustion air is conducted through the secondary airflow channel to reach the second air and fuel mixing region without passing through the air orifices formed in the orifice plate.
The line burner further includes chimney means fixed to the burner housing for providing a flue to carry off inert gases collecting in the first and second air and fuel mixing regions. The chimney means includes a pair of extension plates aligned in spaced apart relation to define the flue. The pair of fuel gas manifolds are situated to lie in the flue between the pair of extension plates. The mounting means connects each of the fuel gas manifolds to a companion one of the extension plates.
Each fuel gas manifold is situated to lie adjacent to the first means and one of the second means in heat transferring relation. This arrangement advantageously permits heat energy from the fuel gas supplied to the fuel gas manifolds to be transferred to the combustion air conducted through the first and second means to cool the fuel gas manifolds during operation of the line burner.
Angle irons are arranged on the outside of the fuel gas manifolds and spaced from them. To enable a favorable arrangement of the extension plates and also to achieve a pair of combustion air flow channels around the combustion gas manifolds. The arrangement and extension of these angle irons is such that the combustion air flow will be passed specifically about the fuel gas manifolds and that air is then introduced into the flame area, from a position downstream of the fuel gas manifolds in a second combustion stage. To that end, the angle iron is equipped with a mounting flange. The two flanges protrude from the web in an opposite arrangement.
To make it possible to change the size of the combustion air flow channels according to requirements, means is provided for arranging the angle irons on the burner housing so that the angle irons are detachable and movable transverse to the longitudinal direction. The combustion air flow channel which partly encompasses the fuel gas manifolds can then be so varied, through loosening and moving the angle irons, that either more or less combustion air will pass through this channel and be directed at the flame. A flow-diverting flange of the angle iron may additionally feature subdivisions or appropriate webs for specifically dividing the airflow that leaves the combustion airflow channel.
The invention is specifically characterized by providing a burner which under unfavorable conditions, specifically at high CO.sub.2 and H.sub.2 O contents, can be operated safely. A surprising multiple result is achieved in that a backup of inert gas into the area of the burner of the flame is precluded, simultaneously through the arrangement of extension plates and the specific routing of the combustion air flow. The specific routing of the combustion airflow results in further effects insofar as a cooling of the combustion air devices is accomplished along with a combustion in two steps, since the combustion airflow channel is arranged spaced behind the orifice plate for the combustion air and once again feeds combustion air to the flame. A distinct reduction of the NO.sub.x content of such gases is thus surprisingly guaranteed. Especially in the desulfurization of flue gas in power and similar plants, considerable problems existing there can be solved this way, with the prior design of the burner permitting a favorable integration in the new development.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.